It has long been considered desirable for the starting and operating circuits of gaseous discharge lamps to incorporate circuitry for automatically lighting an auxiliary lamp when the gaseous discharge lamp is extinguished. Examples of such circuits are found in U.S. Pat. Nos. 3,976,910, 3,611,432 and 3,517,254, the disclosures of which are hereby incorporated by reference.
Previous auxiliary lighting circuits, however, are severely limited in their range of application. This is because those circuits are designed to measure specific voltage levels in order to determine whether the gaseous discharge lamp is operating or not. From that determination, the auxiliary lighting source is either energized or maintained in an off state. Voltage levels of gaseous discharge lamp operating circuits vary greatly, however, depending upon the type of lamp (e.g., metal halide or high pressure sodium), the voltage of the power source, and the specific design of the operating circuit. Indeed, most of the previous auxiliary lighting circuits are designed as an inherent part of the main lamp operating circuit and, therefore, have no general applicability to other lamps.